The present disclosure relates to processes for the preparation of a latex by, for example, the emulsion polymerization of monomer in the presence of an odor-reducing compound such as bismuth subsalicylate, as well as to latex and toner compositions formed thereby.
The present disclosure is generally directed to latex and toner processes, and more specifically to processes that utilize emulsion polymerization to form a latex and aggregation and coalescence or fusion of the latex, colorant, such as pigment, dye, or mixtures thereof, and optional additive particles to form a final composition such as a toner composition. In embodiments, the present disclosure is directed to latex emulsion processes and aggregation and coalescence processes with colorant particles, and wherein an odor scavenging additive is used to remove odor-causing species. The latex can in turn be used for forming a toner composition, in a subsequent aggregation or coalescence process. The resulting toners can be selected for known electrophotographic imaging and printing processes, including digital color processes, and more specifically these toners are especially useful for imaging processes, especially xerographic processes.
In imaging systems, especially color systems, small sized toners of, for example, from about 2 to about 8 microns can be of value for the achievement of high image quality for process color applications. It is also important to have a low image pile height to eliminate, or minimize image feel and avoid paper curling after fusing. Paper curling can be particularly pronounced in xerographic color processes primarily because of the presence of relatively high toner coverage as a result of the application of three to four color toners. During fusing, moisture escapes from the paper due to high fusing temperatures of from about 120° C. to about 200° C. In the situation wherein only one layer of toner is selected, such as in one-color black or highlight color xerographic applications, the amount of moisture driven off during fusing can be reabsorbed by the paper, and the resulting print remains relatively flat with minimal paper curl. In process color where toner coverage is high, the relatively thick toner plastic covering on the paper can inhibit the paper from reabsorbing the moisture, and cause substantial paper curling. These and other imaging shortfalls and problems are avoided or minimized with the toners and processes featured herein.
Also, it may be useful to select certain toner particle sizes, such as from about 2 to about 12 microns, with a high colorant, especially pigment loading, such as from about 4 to about 17 percent by weight of toner, so that the mass of toner necessary for attaining the required optical density and color gamut can be significantly reduced to eliminate or minimize paper curl. Lower toner mass also ensures the achievement of image uniformity. However, higher pigment loadings often adversely affect the charging behavior of toners. For example, the charge levels may be too low for proper toner development or the charge distributions may be too wide and toners of wrong charge polarity may be present. Furthermore, higher pigment loadings may also result in the sensitivity of charging behavior to charges in environmental conditions, such as temperature and humidity. Toners prepared in accordance with the processes featured herein minimize, or avoid a number of these disadvantages.
There is illustrated in U.S. Pat. No. 4,996,127, the disclosure of which is totally incorporated herein by reference, a toner of associated particles of secondary particles comprising primary particles of a polymer having acidic or basic polar groups and a coloring agent. The polymers selected for the toners can be prepared by an emulsion polymerization method. It is indicated that the toner can be prepared by mixing the required amount of coloring agent and optional charge additive with an emulsion of the polymer having an acidic or basic polar group obtained by emulsion polymerization.
In U.S. Pat. No. 4,983,488, the disclosure of which is totally incorporated herein by reference, there is disclosed a process for the preparation of toners by the polymerization of a polymerizable monomer dispersed by emulsification in the presence of a colorant and/or a magnetic powder to prepare a principal resin component, and then effecting coagulation of the resulting polymerization liquid in such a manner that the particles in the liquid after coagulation have diameters suitable for a toner. In U.S. Pat. No. 4,797,339, the disclosure of which is totally incorporated herein by reference, there is disclosed a process for the preparation of toners by resin emulsion polymerization wherein certain polar resins are selected; and in U.S. Pat. No. 4,558,108, the disclosure of which is totally incorporated herein by reference, there is disclosed a process for the preparation of a copolymer of styrene and butadiene by specific suspension polymerization.
Polyester based chemical toners substantially free of encapsulation are also known, reference U.S. Pat. No. 5,593,807, the disclosure of which is totally incorporated herein by reference, wherein there is disclosed a process for the preparation of a toner comprised of a sodio sulfonated polyester resin and pigment, and wherein the aggregation and coalescence of resin particles is mediated with an alkali halide. Other U.S. patents that may be of interest, the disclosures of which are totally incorporated herein by reference, are U.S. Pat. Nos. 5,853,944; 5,843,614; 5,840,462; 5,604,076; 5,648,193; 5,658,704; and 5,660,965.
In U.S. Pat. No. 4,837,100, the disclosure of which is totally incorporated herein by reference, there is illustrated, for example, an electrophotographic developer comprising a carrier, toner particles positively chargeable by friction with the carrier, fine particles of hydrophilic alumina, and fine particles of one of tin oxide, hydrophobic silica and titanium dioxide, and wherein the hydrophilic alumina fine particles are present in an amount of from about 0.1 to about 3 percent by weight based on the weight of toner particles. The alumina particles of this patent can be selected for the toners and processes featured herein in embodiments thereof.
Emulsion/aggregation/coalescence processes for the preparation of toners are illustrated in a number of Xerox Corporation patents, the disclosures of each of which are totally incorporated herein by reference, such as U.S. Pat. Nos. 5,290,654, 5,278,020, 5,308,734, 5,370,963, 5,344,738, 5,403,693, 5,418,108, 5,364,729, and 5,346,797; and also of interest may be U.S. Pat. Nos. 5,348,832; 5,405,728; 5,366,841; 5,496,676; 5,527,658; 5,585,215; 5,650,255; 5,650,256; 5,501,935; 5,723,253; 5,744,520; 5,763,133; 5,766,818; 5,747,215; 5,827,633; 5,853,944; 5,804,349; 5,840,462; 5,869,215; 5,863,698; 5,902,710; 5,910,387; 5,916,725; 5,919,595; 5,925,488; 5,858,601, and 5,977,210. The appropriate components and processes of the above Xerox Corporation patents can be selected for the processes featured herein in embodiments thereof.
Despite these various processes for forming latexes and toners, a problem remains in the final compositions. In particular, many of the final compositions exhibit undesirable odors. For example, when many toner compositions are fused to a print medium, i.e., when the toner composition is heated to cause fusing, the toner compositions emit a strong, undesirable odor. Such odors may be caused by the emission of volatile organic and/or sulfur-containing compounds, which are predominantly present in the toner composition as originating in the latex used to form the composition. Such odors can also be noticed in the toner compositions at room temperature, such as during processing, toner composition replacement, and the like. While not adversely affecting print quality, these odors are undesirable to many production personnel and end-use customers. Many attempts have been made to address this odor issue, although with varying effect.
For example, U.S. Pat. No. 5,928,829 discloses toner processes where a latex is formed by polymerization of monomer in the presence of a catalytic chain transfer component and an initiator. The process is described to provide latex compositions that are free of solvents, and which thus exhibit decreased or minimal odor.
U.S. Pat. No. 6,475,691 also discloses processes for the preparation of toner involving (i) aggregating a colorant dispersion containing a suitable surfactant with a latex emulsion containing an anionic surfactant, a nonionic surfactant, and a water miscible chain transfer agent, or a nonionic surfactant with chain transfer characteristics to form toner sized aggregates; (ii) coalescing or fusing said aggregates; and optionally (iii) isolating, washing, and drying the resulting toner. The patent describes that the use of the chain transfer agent helps to reduce odor by avoiding the use of costly and hazardous odor producing components, such as carbon tetrabromide, alkyl thiols such as butanethiol and octanethiol, and the like.